Shock-absorbing spring clamp for electric induction apparatus

ABSTRACT

An improved clamping means for retaining in position the windings of liquid-immersed electric induction apparatus of the high current type. Shock-absorbing spring clamps interposed between one end of power transformer windings and a portion of the frame resiliently exert a follow-up clamping force on the windings under steady state conditions and resist by dashpot action any transient or shock force tending to cause winding displacement, such as electromagnetic force under short circuit conditions.

United States Patent [191 Wilketal.

[ Nov. 13, 1973 SHOCK-ABSORBING SPRING CLAMP FOR ELECTRIC INDUCTION APPARATUS [75] Inventors: Stanley H. Wilk, Dalton; Bernard W. Lord, North Adams, both of Mass.

[73] Assignee: General Electric Company,

Pittsfield, Mass.

[22] Filed: Sept. 1, 1972 [21] Appl. No.: 285,723

52 us. Cl. 336/197, 336/210 [51] Int. Cl. H011 27/30 [58] Field of Search 3116/58/94, 197, 336/210 [56] References Cited UNITED STATES PATENTS 1,311,507 7/1919 Harlow 336/197 1,539,670 5/1925 Hendricks, Jr 336/197 X 3,156,885 11/1964 3,467,932 9/1969 3,172,064 3/1965 Schmid et a1. 336/197 Primary Examiner-Thomas J. Kozma Attorney-Francis X. Doyle et al.

[57] ABSTRACT An improved clamping means for retaining in position the windings of liquid-immersed electric induction apparatus of the high current type. Shock-absorbing spring clamps interposed between one end of power transformer windings and'a portion of the frame resiliently exert a follow-up clamping force on the windings under steady state conditions and resist by dashpot action any transient or shock force tending to cause winding displacement, such as electromagnetic force under short circuit conditions.

4 Claims, 4 Drawing Figures 16 A, a g

SHOCK-ABSORBING SPRING CLAMP FOR ELECTRIC INDUCTION APPARATUS BACKGROUND OF THE INVENTION This invention relates to liquid-immersed electric induction apparatus of the type comprising a magnetic core about which one or more conductive windings are positioned, as in power transformers, reactors or the like. More specifically, this invention relates to an improved means for clamping and retaining the windings of large electric power transformers immersed in oil or other insulating liquid.

It is well known that under the stress of the heavy overload currents or short-circuit currents which may occur in a transformer, magnetic interaction between the transformer winding turns creates forces which tend to expand the winding axially and displace the winding with respect to the core. Windings must be firmly clamped in position both to resist such magnetic shock and also to prevent their displacement as a result of mechanical vibration in transport and electrical vibration under normal load conditions. One retaining structure previously known is a fixed clamp interposed between one end of the winding and a fixed part of the transformer frame or base. Such fixed clamps have not been entirely satisfactory, however, in that if the winding insulation shrinks or compresses over a period of time, the windings are no longer securely retained in position. Spring-loaded devices have also been used in the past to obtain follow-up pressure on windings. In such devices, however, the springs have had to be inordinantly large in order directly to resist deformation forces resulting from short circuit currents. Also, in many instances, a great many clamping devices have been required, substantially contacting all free areas of each winding.

Accordingly, it is a principal object of this invention to provide an improved shock-absorbing spring clamp for the windings of liquid-immersed electric induction apparatus.

It is a more particular object of this invention to provide improved resilient clamping means for the windings of liquid-immersed power transformers or the like which provides continuous spring pressure on the windings, despite gradual shrinkage or compression of winding insulating, and separate shock-absorbing means to relieve the spring of sudden massive shock loads.

It is still another object of this invention to provide a shock-absorbing winding clamp for transformers in which initial adjustment and clamping of the windings is simply and inexpensively accomplished.

A further object of this invention is to provide a novel shock-absorbing spring clamp for transformer windings using special support plates to improve the utilization of space in the core and provide more efficient use of the winding clamp.

SUMMARY OF THE INVENTION In carrying out this invention in one preferred embodiment, a magnetic core and coil assembly is provided, immersed in insulating liquid. The coil or winding is firmly seated at one end of the core as a base, or frame, and a bearing ring or support plate is seated against the other movable end of the coil. The bearing plate is spaced from the apparatus frame and a plurality of shock-absorbing spring clamps are interposed between the plate and frame. In each clamp, a cylinder having a spring-pressed piston presses against the bearing plate to exert continuous clamping force upon the coil under steady state conditions. Each cylinder is provided with a restricted aperture to permit limited ingress and egress of the ambient liquid so that the liquid imposes no appreciable resistance against the gradual piston movement. However, any. transient displacement force, as due to mechanical shock or electrical short circuit, is opposed by the dashpot action of the piston and cylinder. Thus the spring need be only sufficiently strong to initially compress the coil and retain it in position in normal operation, but need not be so strong that it can resist massive short circuit or other shock forces. A secondary support plate, inclined to fit under the core is interposed between the bearing ring and the spring-pressed cylinder.

The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed'that this invention and the manner in which its objects and advantages are obtained, as well as other objects and advantages thereof, will be better understood from the following detailed description of a preferred embodiment, especially when considered in the light of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partial side elevational view of a portion of a transformer embodying the clamping arrangement according to this invention, the casing being partly broken away to expose the interior structure;

FIG. 2 is a fragmentary top view of the clamping assembly of FIG. 1;

FIG. 3 is a sectional view taken on the line 3-3 of FIG. 1; and

FIG. 4 is an axial cross-sectional view of a single one of the shock-absorbing spring clamps utilized in the as semblies of FIGS. 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawing, and more particularly to FIG. 1, there is shown a portion of a power transformer 10 comprising a casing 12 having a cover 14 and filled with electrical insulating liquid 16. Disposed in casing 12 is magnetizable core 18 having a vertical leg 20 surrounded by coils or windings 22. The tranformer windings 22 are rigidly seated at its lower end against suitable frame structure such as a lower core clamp (not shown). Axially adjacent the upper end of the winding 22 is a centrally apertured support plate or bearing ring 24. This plate 24 is preferably formed of non-metallic material such as wood, fiber glass, epoxy resin or a resin-filled wood or paper. However, plate 24 may be constructed of steel or similar metal if strength and electrical properties so require, provided that it is split radially or otherwise to break the electrical circuit to prevent induced circulating current and suitably spaced from the coil assembly 22 by insulating spacers. If desired, spacers may be interposed between the plate 24 and the movable end of coil 22 to provide for passage of liquid therebetween.

As can best be seen from FIG. 3, bearing ring or support plate 24 is a ring member, preferably non-metallic bearing against the upper end of coil assembly 22. In the preferred embodiment of this invention, secondary support plates or bearing members 26 are provided, spaced about and resting on support plate 24. In the preferred form of the invention, as shown in FIG. 2, four secondary support plates 26 are provided, equally spaced about bearing ring or support plate 24. As can best be seen in FIG. 3, each secondary support plate 26 is beveled or tapered at its inner edge 28. This enables the inner plates 26 to fit under the yoke portion 30 of core 18. As will be understood, by providing large area secondary support plates 26, with tapered portions 28, a very thin bearing ring 24 may be used, to conserve space which is at a premium in the core window and still provide a strong clamp support for winding assembly 22.

Each secondary support plate 26 is pressed axially against bearing ring 24 and therefore against windings 22 by a spring-loaded clamp assembly 32. Each clamp assembly 32 is slidably mounted in a flange 34 or 36 which forms a part of upper core clamp 38. Each clamp assembly 32 has a metal foot member 40 which bears on the top of a secondary support plate 26, as shown.

Each clamping assembly 32 includes a cylinder 42 which is closed at its lower end by the foot 40. As will be understood, foot 40 can be made integral with cylinder 42, or it may be welded to the lower end, as indicated at 44. A small opening 46 is formed in cylinder 42, as shown in FIG. 4. Mounted in cylinder 42 is a spring 48 which bears against foot 40. The upper end of each cylinder 42 is open and slidably mounted therein is piston 50 having a ring seal 52. The spring 48 is confined between piston 50 and foot 40. Foot 40 is made as large as possible in conjunction with the top of support 26 to provide maximum clamping on windings A piston rod 54 extends from piston 50 through a threaded flange 56 on core clamp 38 with locknut 58. The upper end of piston rod 54 is threaded as shown at 60 and is provided with a hex head top 62. As will be understood, by use of head 62, piston rod 54 may be four clamping assemblies 32 pressing against'the four secondary support plates 26 (shown in FIG. 2) in the manner above described. Of course, it will be understood that adjusting screws operating on piston rods 54 may be used, or other means may be provided to compress springs 48. The springs 48 will provide follow up pressure on windings 22 should the windings 22 settle or shrink in use. The springs 48 will also prevent displacement of windings 22 due to vibration.

From the above, it will be understood that springs 48 are sufficiently strong to compress the coil 22 to the desired degree and to hold it firmly in position against the lower yoke clamp. As will now be described, springs 48 need not be strong enough to fully resist short-circuit electromagnetic forces which tend to expand the coil 22 axially.

The entire casing 12 is filled with an insulating dielectric liquid 16 which may suitably be oil or askarel. The core 18 and coil assembly 22 is immersed in the liquid 16, so that the clamping assemblies 32 are below the liquid level. Thus the cylinders 42 are filled with liquid 16, and the liquid 16 is free to enter or leave each cylinder 42 at a restricted rate through the aperture 46 in each cylinder 42. Presence of liquid 16 in each cylinder 42 and the restricted opening 46 in each cylinder 42 combine to resist any sudden movement between cylinders 42 and their associated pistons 50 by shockabsorbing dashpot action.

It will now be understood by those skilled in the art that the cylinders 42 may either be open at one end, as shown, to provide free access of ambient liquid to one side of the piston 50, or may extend beyond the piston 50 to form an apertured chamber at both sides thereof. In case the cylinder forms a chamber at each side of the piston, each chamber must be apertured to provide for ingress and egress of liquid, and at least one aperture must appreciably restrict the flow of liquid.

In operation, initial adjustment of the clamping assemblies 32 is effected by tightening down the pistons 50 thus compressing the clamping springs 48 to apply the desired force against the bearing ring 24. Because this clamping force is resiliently applied by the compression springs 48, the pistons 50 and bearing ring 24 will follow long-term movement of the upper end of the coil 22 as the winding insulation shrinks or otherwise further compresses over a period of time. In such gradual movement the liquid in each shock-absorbing cylinder 42 does not inhibit movement between each cylinder 42 and its associated piston 50, because the slow rate of movement required can be accommodated by flow of liquid through the cylinder apertures 46.

If, however, the transformer windings 22 attempt suddenly to expand axially, as by electromagnetic action due to sudden imposition of overload or short circuit on the transformer, such expansion is resisted by the shock-absorbing dashpot action of the cylinder 42 and piston 50 without depending entirely upon the resistance provided by the clamping spring 48. Such shock-absorbing action occurs because the aperture 46 is made of such size that no appreciable amount of oil can escape from the cylinder during a momentary application of force. Thus, it is possible to utilize in shockabsorbing clamps 32 clamping spring 48 which are only sufficiently strong to compress the windings 22 and hold them firmly in place under normal load or normal transit conditions. It is not necessary to provide that excessive amount of spring force which would be necessa y in the absence of dashpot action to effectively resist short-circuit forces or massive mechanical shock forces.

While there has been shown and described the present preferred embodiment of this invention, it will be understood by those skilled in the art that various changes may be made in various details without departing from the spirit and scope of this invention, particularly as it is defined in the appended claims.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. ln anelectrical induction apparatus including a core, a core clamping frame and a conductive coil mounted on a portion of said core and fixedly seated at one end on said frame, resilient clamping means mounted between said frame and the other end of said coil, a bearing ring mounted on said other end of said coil and axially aligned therewith, a plurality of support plates mounted on said bearing ring, said resilient clamping means comprising a plurality of cylindrical members movably mounted in said frame, one end of each of said plurality of cylinders closed by a metal foot, each said metal foot engaging one of said plurality of support plates, a compression spring mounted in each of said cylinders, one end of said spring engaging said metal foot, a piston movably mounted in each said cylinder and engaging the other end of said spring, a piston rod secured to each said piston, means adjustably securing each said piston rod to said frame, whereby each said piston rod is adjustable to cause each piston to compress each said spring to provide resilient compressive force on said conductive coil, arestricted aperture in each said cylinder between said piston and said foot, and electrical insulating liquid filling each cylinder between said piston and said foot whereby said piston, said cylinder and said liquid operate by dashpot action to relieve said spring of shock forces suddenly applied to said cylinder by electromagvided spaced equally about said bearing ring. 

1. In an electrical induction apparatus including a core, a core clamping frame and a conductive coil mounted on a portion of said core and fixedly seated at one end on said frame, resilient clamping means mounted between said frame and the other end of said coil, a bearing ring mounted on said other end of said coil and axially aligned therewith, a plurality of support plates mounted on said bearing ring, said resilient clamping means comprising a plurality of cylindrical members movably mounted in said frame, one end of each of said plurality of cylinders closed by a metal foot, each said metal foot engaging one of said plurality of support plates, a compression spring mounted in each of said cylinders, one end of said spring engaging said metal foot, a piston movably mounted in each said cylinder and engaging the other end of said spring, a piston rod secured to each said piston, means adjustably securing each said piston rod to said frame, whereby each said piston rod is adjustable to cause each piston to compress each said spring to provide resilient compressive force on said conductive coil, a restricted aperture in each said cylinder between said piston and said foot, and electrical insulating liquid filling each cylinder between said piston and said foot whereby said piston, said cylinder and said liquid operate by dashpot action to relieve said spring of shock forces suddenly applied to said cylinder by electromagnetic action of said coil.
 2. An electromagnetic induction apparatus as set forth in claim 1 in which said plurality of support plates are equally spaced about said bearing ring.
 3. An electromagnetic induction apparatus as set forth in claim 1 in which said plurality of support plates have an inclined portion, said inclined portion extending under a portion of said core.
 4. An electromagnetic induction apparatus as set forth in claim 1 in which four support plates are provided spaced equally about said bearing ring. 